Getting Started: Breeding Mice

Selection of Parents
I think at one time or another we have all wished that we could choose our parents… and breeding mice is a rare situation in that we can. The mice we choose are very important for many reasons.

• Parenting Ability: Obviously it’s very important that the babies will be looked after when they are born. If you choose a skittish or nervous doe she might not do as well and be reluctant to let you handle the litter. In the worst case she may reject the babies due to lack of trust (if they smell of their human owner too much too soon or have been frequently disturbed) and they will either starve or the mother’s instinct will tell her to eat her babies.

• Hereditary Traits: If there are traits you do not want to pass on e.g. whisker biting, barberism, or general unfriendliness then this is the time to realise this and isolate those mice from your breeding programme. If you are still keen despite some problems with your desired mouse then you will have to weigh up the good and bad points. Most of all you must be concerned with the well being of the animal. However, some may not consider breeding certain mice because they intend to show the offspring (see below).

• Colour Genetics: There have been volumes written on this. It basically comes down to working out what colour the offspring from a mating will be, using the parents’ genetic make-up. For example, if you were breeding two self-blacks who both had a gene for self-black colouring and a gene for self-lilac colouring (taking SB as the dominant gene and SL as the recessive), your litter is likely to be:

In other words, it is likely that one in four of the babies will be a self-lilac. This sort of calculation can be used to ‘improve’ show stock lineage and eliminate undesirable features such as short tail or small ears, as well as various markings and colourings.

• Illness/Health Problems: My housemate once begged me repeatedly to breed her favourite of my mice, Niamh, because she wanted to keep the litter. Despite her incessant pleading I had to refuse because the mouse in question has a kinked tail. As many readers will be aware, this could have led to painful spinal problems in her young. Other problems that are important to avoid propagating are waltzing and generally weak constitutions.

Have You Got the ‘Right Stuff’?
Once you have selected your best buck and doe (or trio; two does and a buck) then you are a step closer. But first you have to make sure that apart from a breeding pen you will also be able to house the babies for at least five weeks before they go to new homes. They need to stay with their mum all this time (although boys may be separated from the girls and mum after four weeks). Breeders have to make sure that the mother is not too bored but doesn’t have a cage filled with toys that will cause her to become too active when pregnant, or cause a risk to the litter when it is born. Personally, I would suggest a couple of wide cardboard tubes and a cut up egg box (which she will also shred to make her nest) make up her cage furniture. I take the wheel out in the last couple of weeks of pregnancy until the babies are around three weeks old, just to avoid any accidents.

So… Shall We Do It?
When you have met the criteria outlined for selecting your mice and think you are ready to breed, there are a few rules you would do well to follow.

1. Make sure your breeding pen is big enough for the two mice to live in for a week or so. They will not thank you if they are confined in a tiny space, and will probably not get on as well either!

2. Clean out the tank thoroughly so it does not smell of a particular mouse. Provide plenty of bedding, food and water.

3. You may want to introduce the doe and buck on your hands before putting them in the tank together. If not, put the buck in first as does will defend their territory against any invading bucks!

4. Make sure the tank is not in a draught or direct sunlight (as with any tank). Try not to disturb them too much for the first few hours they are together to allow them to adjust to their new situation. They will probably sniff each other and the male may chase the female around but this is normal. If the female is in heat she can become pregnant straight away!

When is the Best Time?
There are some things you should know when you intend to breed mice that will make your life a lot easier and avoid unexpected litters. Does come into heat on average every four or five days, during which time they can get pregnant. They can also become pregnant again immediately after giving birth on their postpartum oestrus (meaning they immediately come back into heat), so if you do not want two litters back to back, which is inadvisable, you must remove the male before the birth. However, if you do decide to leave the male in with the female, he will make a good father and help the mother to look after her babies. Having said this, you must take into account that the female will be rearing two litters at the same time, which will put extra strain on her body – especially in regard to her milk-producing abilities.

Midwife?
When the mouse gives birth she will need no help from you and should be left undisturbed. If she is in a quiet and darkish place she should be just fine on her own. If she is living with other does they may help her, acting as midwife and sharing the care of the litter. If anything goes wrong and the mother abandons her babies they can be fostered to another doe that has babies of the same age, who may adopt them and continue to raise them. Otherwise, it is very hard to raise orphaned mice, as they have to be fed at least every two hours to remain alive. However, it has been done.

Most does give birth between 10pm and 2am, when mice tend to be the most active. The babies announce their arrival (and so may mum) by squeaking from within the nest. At this point they should not be disturbed, but left alone for at least a day. It depends on the doe as to when you look at the babies for the first time. If she trusts you, it may be possible to look as early as day one, but if in doubt wait until day three. By this time you really should check the nest if only to make sure that no babies were stillborn.

Technique
When you want to look at the babies you must wait until the mother leaves the nest voluntarily and remove her from the tank. This way she cannot see you handling her babies and get distressed. A new mum often welcomes the break and relishes the chance to run about in her ball after being stuck in with her babies for three days! When mum is safely out of the way, it is advisable to rub your hands in the dirty bedding to make them smell more mousy and less human. Then you can gently lift up the bedding and look at the babies, pick them up etc. Just remember that it is important that they stay warm so do not keep them out of their nest for too long.

Continuing Care
Your part may be relatively small but it is important. You must make sure that mum has plenty of food and water. It is a good idea to give her fattier food than usual while she is pregnant and lactating. Otherwise, keep handling the babies and enjoy your litter!

Age at weaning: 3.5 weeks on average
Age at sexual maturity: 4-6 weeks
Recommended breeding age: Does – 3 months, Bucks – 10 weeks onwards
Gestation period: Average 19-21 days
Average time of birth: 10pm – 2am
Fur begins to grow: 7 days onwards
Eyes open: 13 days onwards

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